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2003 chevy trailblazer_lt
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Discussion Starter · #1 ·
I've followed this forum for years and have always been able to repair myself up until now without asking for assistance from this fine community. My 03 TB w/ 284K miles (orig owner) has a misfire / roughness on cyl #1 that appears only at (or near) idle rpms. Mileage has dropped about 2 mpg. [I have an Autel scanner for diag.] I've swapped the Cyl #1 & #2 coils and get the same misfire on Cyl #1. As a result of the misfire, fuel trims go slightly negative. So I removed the throttle body, cleaned it (it wasn't too dirty as I did this about 50K miles prior), reinstalled, reset fuel trims with the scanner and still have the misfire at idle. Next, I replaced the (original) crankcase vent hose with the ACDelco p/n 12575660. Here is where it may get interesting...I took a piece of solid copper wire and gently slid it in the horizontal tube and it stops about 4 inches in as if I am hitting the aluminum casting. The tube portion seems wide open without any restriction using the copper wire probe method. I sprayed some cleaner in the tube, then attached a long hose to blow by mouth. It's very hard to detect if there is any orifice opening. Is it very small and undetectable using this method? I also took a battery/portable compressor, set it to 5 psi and attempted to blow through the orifice with undetermined results. Does anyone know how large the orifice opening is? By the way, when I remove the oil cap I really don't detect any suction on my palm with the motor running. Thanks in advance!
 

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@ hpgrisco,

I've followed this forum for years and have always been able to repair myself up until now without asking for assistance from this fine community.

My 03 TB w/ 284K miles (orig owner) has a misfire / roughness on cyl #1 that appears only at (or near) idle rpms.

Mileage has dropped about 2 mpg. [I have an Autel scanner for diag.] I've swapped the Cyl #1 & #2 coils and get the same misfire on Cyl #1.

As a result of the misfire, fuel trims go slightly negative.

So I removed the throttle body, cleaned it (it wasn't too dirty as I did this about 50K miles prior), reinstalled, reset fuel trims with the scanner and still have the misfire at idle.

Next, I replaced the (original) crankcase vent hose with the AC Delco p/n 12575660.

Here is where it may get interesting...I took a piece of solid copper wire and gently slid it in the horizontal tube and it stops about 4 inches in as if I am hitting the aluminum casting.

The tube portion seems wide open without any restriction using the copper wire probe method.

I sprayed some cleaner in the tube, then attached a long hose to blow by mouth.

It's very hard to detect if there is any orifice opening. Is it very small and undetectable using this method?

I also took a battery/portable compressor, set it to 5 psi and attempted to blow through the orifice with undetermined results.

Does anyone know how large the orifice opening is?

By the way, when I remove the oil cap I really don't detect any suction on my palm with the motor running.

Thanks in advance!

^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

I had to open up your monoparagraph so it could be read ------


I'm having a really hard time because I'm not sure of which engine you have - as you didn't post that info.

I have a picture of your hose ....

Bicycle part Office supplies Auto part Font Metal

.... but it's not indicative of the engine either.

More information please ....
 

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2003 chevy trailblazer_lt
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Discussion Starter · #3 ·
4.2L.

Yep. That's the hose I just replaced.

I've read many of your other related posts regarding the 4.2L crankcase vent sys.

I was wondering if anyone knew more about the actual orifice construction at the "dirty" hose lower port as well as if a clog here would cause a cyl #1 misfire at idle only.
 

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OK --- now we got some info to work with ....

I'm sure you realize that there are no moving parts in the PCV system on these engines --- and with that information --- the "dirty" or CV-side of the system is subject to collecting gunk that hardens into crust and carbon chunks inside the vacuum side of the system.
It is also (unfortunately) the lowest part of the circuit and gunk slithers downhill .... there's that!​

As you also know, that upper "clean side" of the system is called the "KV-side" or "Atmospheric side" --- and it is designed as a restriction on the whole PCV system --- that terminates at the intake runners for the individual cylinders.

The most common failure is at those runners --- where --- when the engine is shut off after a hot run ---- that vaporous gunk then coagulates and solidifies because the more volatile esters readily boil off, leaving carbon behind.

Then there's the short-hop runs that never truly get to suck the crankcase vapors from the oil pan, timing cover, block insides and the valve cover.

When these short hops get too much for the system to clean the crankcase well ---- then more gunk forms ---

BUT ---> worse than that ---- the moisture that doesn't get purged, winds up in the oil pan and since oil is lighter than water and it floats under the oil --- the first thing the oil pump picks up next cold start is pure dirty water.

I'm on record saying that the constant cleaning of the throttle body and the constant VVT failures on these engines is a direct function of this water getting sent back into the engine in a homogenized colloid of oil and water.

So --- you had a question about pushing a wire through --- where? I'm not sure I follow that part.

You certainly can use a lot more air pressure than 5lbs!

I used 175lbs to blow out my CV-side after I had performed the Berryman's B12 treatment a few times.
Also note that I really forced that high pressure air into the lower pipe --- (not the upper!) --- on the driver's side of the engine, below the ECM.​

And --- YES --- IF the PCV system is working correctly ---- there will be a true vacuum at the oil filler neck (under the 710 cap) and the dipstick tube --- when the engine's running.

There will also be NO MULM --- for the lack of a better, more descriptive word --- inside the OIL/710 cap --- nor on the dipstick wire (for lack of a better term for what passes as the dipstick on these engines!).

And certainly --- there will be no gunk getting into the sound chamber either.

It seems like you're pretty much up to speed on it so just get it working and you'll be a lot happier when it is so!

Addenda -- unfortunately for us, the vehicle owners --- this PCV system is nominally effective and has to be at 100% efficiency to even make it work at all.

That --- and the true vacuum value after the throttle plate --- is "read" by the MAP and tattles to the ECM --- and it keeps the throttle motor from going WOT unless there's sufficient vacuum to keep the PCV system under at least a prescribed vacuum at all times.

IOW --- you've got to get ahead of- and maintain- free flow of the PCBV at all times.
 

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Oh yeah --- I don't think the PCV can actually pick on a single cylinder.
 

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You swapped coils, but the misfire stayed put. Probably not an ignition problem.

Cranking compression test. I worked on a 400 Ford with 50 psi in one cylinder due to leaking valves. Dead at idle. Ran with more throttle opening/higher load, though.

Fuel pressure test. Find out if that injector is leaking, in addition to verifying proper pressure. Maybe that injector is making that cylinder so over-rich it won't run properly. Did the plug from that cylinder look fouled/carboned?
 

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Another horror could be that the cam has spit a follower --- not a 100% guaranteed thing, but this engine seems to like to spit #1 exhaust followers a lot.
 

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Discussion Starter · #8 ·
I should take a fuel gauge under the vehicle and attach to the port near the fuel filter and test each injector. Since the fuel trims are slightly negative (the PCM is commanding reducing fuel), I believe I know where this is headed.

Cyl #1 is likely leaking some fuel and needs to be replaced. The valve cover gasket is leaking some oil as well.

I'm about to pull the trigger on the monotonous task of taking the valve cover, intake and fuel rail off, cleaning everything well, replace Cyl #1 injector and reassemble. First I have to order parts and any misc tools I might need like a carbide scraper and fuel line removal tool.

Then find a two day window in my schedule and DO IT! :)
 
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